Last updated: 2026-11-04
A round solar panel collects light over a circle, which has 78.5% of the area of a square with the same width. The listed round panels span 0.35 W at 70 mm up to 2 W at 150 mm, at 5 V or 6 V. Match diameter, voltage and connection to your circuit.
You have a round lamp cap, a sensor housing or a pole-top cover, and every solar datasheet you find shows a rectangle. A small round solar panel fits that space directly, but it gives up area compared with a square of the same width, and its voltage depends on how many cells fit inside the circle. A small round solar panel is a photovoltaic board with a circular outline, specified by diameter, rated power, working voltage and connection.
When a round solar panel makes sense
A round solar panel makes sense when the mounting surface is circular, because a circle fills a round lid or recess while a rectangle either overhangs it or leaves part of it empty.
The cost of the shape is geometry. A circle of diameter D has an area of π × D² / 4, which is 78.5% of the D × D square that spans the same width, so about 21.5% of the square's area is given up at every size.
| Diameter | Round area | Square of same width | Area difference |
|---|---|---|---|
| 70 mm | 38.5 cm² | 49.0 cm² | 10.5 cm² |
| 80 mm | 50.3 cm² | 64.0 cm² | 13.7 cm² |
| 90 mm | 63.6 cm² | 81.0 cm² | 17.4 cm² |
| 110 mm | 95.0 cm² | 121.0 cm² | 26.0 cm² |
| 120 mm | 113.1 cm² | 144.0 cm² | 30.9 cm² |
| 150 mm | 176.7 cm² | 225.0 cm² | 48.3 cm² |
The comparison reverses when the space itself is round. The largest square that fits inside a 90 mm circle has a side of 90 / √2, about 63.6 mm, and an area of 40.5 cm², against 63.6 cm² for a round panel that fills the circle. Round lamp tops, sensor housings and pole caps are the typical cases, and a flat rectangular top is the case where the round shape buys nothing.
Round mini solar panels you can order now
Seven round mini solar panels are listed now, spanning 0.35 W at 70 mm up to 2 W at 150 mm, at a working voltage of either 5 V or 6 V.
| Panel | Diameter | Rated power | Working voltage | Current as listed | Connection |
|---|---|---|---|---|---|
| 70 mm 0.35 W round DIY module | 70 mm | 0.35 W | 5 V | up to 70 mA | Rear solder pads |
| 80 mm 0.5 W round panel, 10-pack | 80 mm | 0.5 W | 6 V | 0 to 66 mA, short circuit 80 mA | Attached red and black leads |
| 80 mm 0.5 W round module, single | 80 mm | 0.5 W | 6 V | short circuit 80 mA | Rear solder contacts, no lead |
| 90 mm 0.6 W round panel | 90 mm | 0.6 W | 6 V | 0 to 100 mA, short circuit 120 mA | Rear contact points |
| 110 mm 1 W round DIY module | 110 mm | 1 W | 5 V | up to 200 mA | Rear solder pads |
| 120 mm 1.1 W epoxy round module | 120 mm | 1.1 W | 5 V | up to 220 mA | Rear solder pads |
| 150 mm 2 W round panel | 150 mm | 2 W | 6 V | 0 to 330 mA, short circuit 350 mA | Rear solder contacts |
Voltage follows the cell layout rather than the diameter. The 70 mm, 110 mm and 120 mm panels are 5 V parts, while the 80 mm, 90 mm and 150 mm panels are 6 V parts, so a larger circle does not automatically mean a higher voltage.
Current follows the textbook relation current = power / voltage. A 1.1 W panel at 5 V gives 0.22 A, which matches the 220 mA listed for the 120 mm panel, and a 2 W panel at 6 V gives about 0.33 A, which matches the 330 mA listed for the 150 mm panel.
Six of the seven use polycrystalline cells under an epoxy or PET-laminate face, and the 110 mm panel uses monocrystalline cells with an epoxy-protected surface. Listed weights are about 18 g at 80 mm, 24 g at 90 mm and 70 g at 150 mm.
Connection decides the assembly effort. Only the 80 mm ten-pack comes with attached leads, about 12 to 15 cm long; the other panels in this table are supplied as bare boards, so soldering is part of the build. Round panels with a USB lead are listed separately.
None of them is a charger. A panel generates power in sunlight and stores none, so a rechargeable battery needs a separate charge-control circuit, and voltage, polarity and current should be checked against the circuit before wiring.
Ring, semicircle and cut-out shapes
A ring, semicircle or cut-out panel gives up the cell area removed by the opening and must fit its cells around it, so its voltage depends on how many cells the remaining outline can hold.
The listed ring panel has an outer diameter of 85 mm and an inner opening of 21 mm, rated 0.33 W at 2.75 V nominal with a peak current of about 0.12 A in strong sunlight. Its ring area is π × (42.5² − 10.5²) = 5,328 mm², or 53.3 cm², against 56.7 cm² for a solid 85 mm circle, so the 21 mm hole removes 6.1% of the area.
The listed semicircular panel measures 153 × 73 mm overall with a centred 45 × 30 mm cutout, and is rated 1 W at 18 V. It has a textured ETFE surface and two polarity-marked rear solder pads; the ring uses a matte PET surface with two solder pads. Both are surface-mounted cell builds on a circuit board, and the listings advise protecting them from vibration and impact.
Voltage follows cell count. A silicon cell gives roughly 0.5 V, so a series string reaches its working voltage by adding cells: about 12 cells for 6 V and about 10 for 5 V on that rule of thumb. A single large cell carries high current at about half a volt, so a round or cut-out module that must land in a voltage window needs smaller cells in series, and the outline decides how many fit.
The two listed shaped panels show the spread. The ring is 2.75 V at 0.12 A, and the semicircle is 18 V, which at 1 W means a current near 1 / 18 = 56 mA. On one past project with a narrow outline, the answer was a lower-voltage board paired with a boost controller rather than forcing a high-voltage cell layout into the space.
Check both diameters against the installation: the outer edge needs clear surface, and the opening must clear anything that passes through the middle.
Curved and tube-wrap panels: what bends and what does not
A crystalline flexible panel bends only over a large radius, and a tight curve such as a small-diameter pole needs thin-film material instead.
Flexible does not mean rollable. A crystalline panel can take a slight bend and be bonded to a gently curved surface, but hard bending cracks cells inside the laminate, and a panel left flat lasts longer. Where the surface curves tightly, the options are thin-film material or a flat panel on a flat facet.
A cylinder never faces the sun all around, and a wrap shows the cost in numbers. Take a pole 60 mm in diameter and a 200 mm wrap height as assumed inputs.
The wrapped area is π × 60 × 200 = 37,699 mm², or 377 cm². Only the half facing the sun is lit, and half the wrapped area is 188.5 cm², but cells near its edges sit at steep angles to the rays.
The effective collecting area with the sun square on the side of the pole is the projected rectangle, 60 × 200 = 12,000 mm², or 120 cm². That is 1/π, or 31.8%, of the wrapped area, so the wrap collects about a third of what the same area of flat panel pointed at the sun would collect.
Series wiring adds a second penalty. A series string is held to its weakest cell, so shaded cells on the far side of a wrap can pull down the current of the whole string.
Cylindrical panels are mostly used for styling. If energy is the goal, a flat round panel tilted toward the sun gives more output from less area, and on a small curved carrier the usable flat area, not the panel rating, caps the power.
What to send for a custom shape
A custom-shape panel starts from a dimensioned drawing with keep-out zones, because the standard cell sizes decide how much of the outline can be filled.
Prepare these six items for a request on the custom mini solar panels page:
- A dimensioned drawing with the outline, the position and size of any hole or arc, and the tolerances you can accept.
- Keep-out zones for screws, lenses, antennas, cables and any part that must pass through the panel.
- The working voltage your circuit expects and the current it draws, since voltage fixes the number of cells in series.
- The mounting surface: flat or curved, the radius of the curve, indoor or outdoor exposure, and any vibration.
- The connection: solder pads, lead length or a connector, with polarity marked.
- The daily energy target. Rated watts × peak sun hours gives the ceiling in watt-hours per day; for a 0.5 W panel and 4 peak sun hours, 0.5 × 4 = 2 Wh, before controller, angle and temperature losses.
Peak sun hours is the daily solar energy on a surface in kWh/m², equal to hours of sunlight at 1,000 W/m². No market figure is given here, so the 4 hours is an assumption for the worked example.
The drawing is checked against standard cell sizes to see what the outline can hold, and whether a particular shape is practical is answered from that check rather than assumed in advance. On one past project, a buyer asked for both a rectangular and a ring layout of the same buoy panel, which made it easier to land on the cheaper geometry.
FAQ
Can a round solar panel charge a battery directly?
No, a round solar panel alone is not a battery charger. The listings state that a panel generates power in sunlight and stores none, and that rechargeable batteries need a separate charge-control circuit. Match the controller to the battery and to the panel's working voltage and current.
Which listed round panel fits a 100 mm recess?
The 90 mm round panel is the largest listed panel that fits a 100 mm recess, with 5 mm of clearance on each side, since (100 − 90) / 2 = 5. The 70 mm and 80 mm panels also fit, and the 110 mm, 120 mm and 150 mm panels are too large. Leave room behind the board for the rear solder pads or contacts.
Is a curved solar panel the same as a flexible one?
No, a flexible panel can follow a curve only within limits. A crystalline flexible panel bends over a large radius and cracks if bent hard, while a tight curve needs thin-film material. Send the surface radius with a drawing so the layout can be checked.
How much energy does a 0.5 W round panel give per day?
At most 2 Wh per day on an assumed 4 peak sun hours, because 0.5 W × 4 h = 2 Wh. Real output is lower, since sunlight intensity, angle, temperature, controller and wiring all reduce it. No market figure is supplied here, so size the panel from your own site's sunlight data.
Next step
Choosing among round, ring and semicircle panels starts from three inputs: the device, the power and the size you need. Note the diameter of the recess, the voltage window of your circuit and the connection you will use, then Browse the matching products.